One important utility for vinyl chloride resins is in the preparation of rigid foamed articles. The articles are manufactured by known methods such as extrusion of a blend of the resin and additives with a suitable chemical blowing agent and choosing the processing temperature such that it is above the decomposition temperature of the blowing agent. The bubbles of gas evolved by the blowing agent are entrapped within the molten resin, thereby forming a cellular structure that are commercially useful articles such as pipe, decorative molding, trimboard, and structural siding. Usually, the polymer is melted at a temperature between 150° and 200° C. and it is necessary to include a stabilizer in the formulation for the purpose of eliminating or at least minimizing the heat-induced discoloration of the vinyl chloride polymer which would otherwise occur at these temperatures. Also, when the decomposition temperature of the blowing agent is much above the processing temperature, activators are employed to hasten the decomposition of the blowing agent and/or lower the blowing agent decomposition temperature. The combination of a blowing agent and an activator increases both the degree and the rate of blowing agent decomposition and potentially the process window of the decomposition. The resultant larger volume of gas generated is desirable, since it reduces the amount of blowing agent required, or can result in lower density foam at similar blowing agent use levels.
It is known that a variety of organotin compounds, particularly dibutyltin derivatives of mercaptocarboxylic acid esters, will impart useful levels of heat stability to vinyl chloride polymers. It is also known that organotin chlorides work well by themselves or in combination with organotin carboxylates as activators for typical blowing agents such as azodicarbonamides, 5-phenyl tetrazole, and benzene sulfonylhydrazide.